Single-Entry AXI-Stream Buffer

Accept an input when s_valid and s_ready are both 1 on a rising edge. Hold it at the output until transferred (m_valid && m_ready).

• s_ready is 1 when the buffer is empty or the output will be consumed on the next edge.
• While the output is stalled, m_valid and m_data remain stable.
• Synchronous active-high reset empties the buffer.